1. Field of the Invention
The present invention relates to a library system for storing a plurality of information recording media such as magnetic tape cartridges and for recording information on any selected one of the recording media or playing back any selected one of the recording media.
2. Description of the Related Art
Conventionally, a large amount of information used for processing with a computer was stored with the use of magnetic tapes. Recently, due to the wide spread use of computers, the amount of information to be processed by computers has drastically increased, so that the number of magnetic tape cartridges used for storage of the increased information has also increased drastically. Under this situation, there has been an increasing need for a fully automated tape library system.
For better understanding, a typical prior art library system is now described with reference to FIGS. 8 and 9 of the accompanying drawings. FIG. 8 schematically illustrates the physical or mechanical arrangement of the library system 51, whereas FIG. 9 is a circuit block diagram representing a control wiring arrangement used for controlling the library system.
As shown in FIG. 8, the library system 51 comprises two shelf-type stockers 66 (only one shown in FIG. 8) each having a plurality of divided compartments for exchangeably accommodating magnetic tape cartridges 64. Each of the stockers 66 is disposed on a respective side of a common transfer track 65 used for movement of two accessors (ACC) 55R, 55L each of which is a carrier robot. The transfer track 65 may include a pair of rails. Each of the ACCs 55R, 55L makes access to each of the stocker compartments for transferring a selected tape cartridge from one position to another within the library system 51 while running on the track 66. The two accessors 55R, 55L, instead of one, are provided for increasing the processing speed while availing one of the accessors for continuation of the process even if the other accessor fails.
In addition to the stockers 66, the ACCs 55R, 55L and the transfer track 65, the library system 51 further comprises two accessor directors (ADR) 52R, 52L (see FIG. 9), two accessor mechanism controllers (AMC) 53R, 53L, two control servos (CSV) 54R, 54L, a cartridge access station (CAS) 56, a direct entry-exit (DEE) 57, and a tapedrive mount unit (TMU) 58. The TMU 58 includes a plurality of drive monitors (DM) 59 and a plurality of magnetic tapedrive units (MTU) 60. The ADRs 52L, 52R are connected to a host computer 62. Though not shown, each of the ADRs 52R, 52L, the AMCs 53R, 53L, the CSVs 54R, 54L, the CAS 56, the DEE 57, the DMs 59and the MTUs 60 has a MPU of its own.
The ADRs 52R, 52L control the AMCs 53R, 53L and the DM 59 under the instructions of the host computer 62. The AMCs 53R, 53L control the CSVs 54R, 54L, the CAS 56 and the DEE 57 under the instructions of the ADRs 52R, 52L. The CSVs 54R, 54L control the drive motors (not shown) of the respective ACCs 55R, 55L under the instructions of the AMCs 53R, 53L. Thus, the ADRs 52R, 52L, the AMCs 53R, 53L, the CSVs 4R, 4L and the ACCs 55R, 55L are connected in hierarchy for controlling purposes.
As shown in FIG. 1, each of the CAS 56, the DEE 57 and the TMU 58 may be respectively installed in a suitable stocker portion not used for cartridge storage. The CAS 56 (cartridge access station) is a unit which is used by the outside operator (not shown) for loading an individual tape cartridge into the library system 51 and for unloading an individual tape cartridge from the library system, whereas the DEE 57 (direct entry-exit) is a unit which is used by the outside operator for loading and unloading a batch of tape cartridges (e.g. ten cartridges) housed in a case.
The TMU 58 (tapedrive mount unit) is a unit for mounting the plurality of DMs 59 (drive monitors) and the plurality of MTUs 60 (magnetic tapedrive units). The DMs 59 monitor the operational states of the MTUs 60, whereas each of the MTUs 60 drives a tape cartridge for recording and playback.
Normally, the right ADR 52R controls the TMU 9 and both of the AMCs 53R, 53L (used also for controlling the CAS 56 and the DEE 57). However, when the right ADR 52R fails, the left ADR 52L takes the place of the right ADR 52R for controlling the TMU 58 and both of the AMCs 53R, 53L.
Though not shown in FIGS. 8 and 9, each of the ADRs 52R, 52L, the AMCs 53R, 53L, the CSVs 54R, 54L, the CAS 56, the DEE 57 and the DMs 59 incorporates a micro processing unit (MPU) and a RS-232C connector of its own. The RS-232 connector is provided for realizing the function of a field maintenance device (FMC). More specifically, when one or more of the ADRs 52R, 52L, the AMCs 53R, 53L, the CSVs 54R, 54L, the CAS 56, the DEE 57 and the DMs 59 fail, a personal computer is connected to the RS-232C connector of each failed element for extracting the operation history data from the relevant MPU. The extracted history data are used for analyzing the cause for the failure and for debugging the MPU.
With the above-described prior art library system 51, however, an operator must go to the location of the library system for connecting a personal computer to the connector of each of the failed elements and repeat a similar operation as many times as the number of the failed elements. Thus, the history extraction is relatively laborious and time-taking.
Further, since each of the ADRs 52R, 52L, the AMCs 53R, 53L, the CSVs 54R, 54L, the CAS 56, the DEE 57 and the DMs 59 does not have a special memory dedicated only for storing the history data, the history data of each MPU need to be stored in a RAM. Thus, unless the history extraction is performed immediately after the occurrence of a failure, the history data once stored in the RAM may be unexpectedly lost by overwriting before analysis if the RAM becomes full. Moreover, the history data stored in the RAM may be also lost at the time of a power failure.